1. Field of the Invention
This invention relates to a proportional control valve for a fluid, and in particular, to a proportional control valve for controlling a supply of gas to a gas water heater used for supplying hot water for a bath, a shower, and in a kitchen.
2. Description of the Related Art
In the gas water heater for supplying hot water for a bath, a shower, and in a kitchen, the control of the water temperature is usually carried out by controlling the water flow rate, i.e., increasing or decreasing same.
In this kind of a gas water heater, however, a problem arises in that, when the water temperature is to be raised, the water flow rate must be reduced, and conversely, when the water temperature is to be lowered, the water flow rate must be increased.
To overcome the above problem, a system for providing hot water at a constant temperature and at a constant rate has been developed. In this system, however, the amount of gas supplied thereto must be controlled by using a proportional control valve, to obtain a desired hot water flow rate while keeping the temperature thereof constant, and further, to control a fluid such as gas, a variable valve such as a governor valve 1 shown in FIG. 1 must be used.
Usually this governor valve 1 has a construction such that a valve portion 15 having a flap 4 is provided in a main passage 13 connecting an inlet 2 and an outlet 3 of a fluid R, and a separated chamber 11 is provided on one side of the valve portion 15 facing the direction from which the fluid R is introduced. Further, two separate subchambers are formed inside the separated chamber 11 by providing a diaphragm 6 between a wall portion of the separated chamber 11 and supporting rod 5 mounted on the flap 4 of the valve portion 15 and movable with the flap 4, to cause one of the subchambers formed between the valve portion and the diaphragm to become a part of the main passage for the fluid. The flap 4 is biased upward by a lower spring 7 attached to the bottom portion of the flap 4 and biased downward by an upper spring 8 attached to the upper portion of the supporting rod 5 through the spring receiver 10.
In this construction, when the fluid R is not supplied to this main passage, i.e., a fluid pressure is not applied to the surface of the flap 4, the valve portion 15 is fully open because the spring force A of the spring 8 is larger than that of the spring force B of the spring 7.
When a fluid R having a regulated pressure, i.e., an initial pressure P.sub.1 is applied at the entrance 2 of the main passage and the fluid R has an output pressure, i.e., secondary pressure P.sub.2, the flap 4 will be brought to a balanced position as indicated by the following equation, ##EQU1## and therefore, a gap 16 is formed between the wall 19 separating the main passage 13 and the flap 4, and the amount of gas passing through the gap 16 is controlled.
In this type of the governor valve, however, the amount of fluid supplied, for example, amount of gas, is set to a constant value when the diameter of a nozzle of a main gas burner is constant.
Namely, when the supply of gas is to be increased, i.e., the initial pressure P.sub.1 thereof is to be increased to raise the temperature of the water, or vice versa, the secondary pressure P.sub.2 of the output gas is generally fixed to a certain value, as shown by a curve c in FIG. 2, because of the spring force applied to the flap 4 of the valve portion 15 by the spring 7 and 8, and thus a precise control as desired cannot be obtained.
Accordingly, to solve the above problem, the screw 9 provided at the top of the spring 8 must be adjusted, for example, the force applied to the flap 4 by said spring 8 must be varied, to obtain the variable curves shown by curves a and b of FIG. 2.
In FIG. 2, curve a shows the curve of the secondary pressure P.sub.2 with respect to the initial pressure P.sub.1 when a strong force from the spring 8 is applied to the flap 4, and curve b shows the curve of the secondary pressure P.sub.2 with respect to the initial pressure P.sub.1 when the lower pressure of the spring 8 is applied to the flap 4.
Nevertheless, this mechanism is manually operated, and therefore, an adjustment as above simultaneously with a detection of the water temperature is difficult, and the device therefore is complex, and therefore, a precise adjustment is difficult and this system is not satisfactory when controlling the temperature of the water.
In another known system, proposed in an attempt to overcome the problems, a plurality of ON-OFF type electromagnet valves are utilized and the gas flow supplied thereto is controlled in multisteps.
In this system, however, the adjustment at each valve can be carried out only in such a way that the force applied to the flap of the valve by the spring is varied by an ON-OFF signal generated when a signal is detected which is higher than a predetermined threshold value with respect to the variation of the detected data for, for example, the water temperature.
Accordingly in this system, the operation of the electromagnet values and the adjustment of the force of the spring is varied only in two steps, and therefore, the amount by which the supply of gas can be varied in this system is limited, and thus it is very difficult to precisely adjust the water temperature.
Further, in the prior art, a transformer is widely used to supply an electric current to the electromagnet values, and this has the disadvantages of a large size and complex control circuit, and the generation of noise at the electromagnet by an ON-OFF operation thereof.